Method of anchoring a first object in a second object

ABSTRACT

A method for joining two objects by anchoring an insert portion provided on a first object in an opening provided on a second object. The anchorage is achieved by liquefaction of a thermoplastic material and interpenetration of the liquefied material and a penetrable material, the two materials being arranged on opposite surfaces of the insert portion and the wall of the opening. During the step of inserting the insert portion in the opening and/or during anchorage a clamping force is applied to opposing surfaces of the second object to prevent the second object from cracking or bulging.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention is in the field of mechanical engineering and constructionand concerns a method for joining two objects. A first one of the objectincludes an insert portion and the other object includes an opening,and, for the two objects to be joined, the insert portion is anchored inthe opening, wherein, in the anchoring area, one of the objects includesa solid material having thermoplastic properties, and the other objectincludes a solid material that is penetrable by the material havingthermoplastic properties when liquefied. The penetrable material of thesecond object is, e.g., fibrous or porous. Especially, it may be awood-based material such as wood, chipboard, etc. The second object maybe a board, and the opening may be an opening in the narrow side face ofthe board.

Description of the Related Art

From e.g. the publications WO 96/01377 (Createc), WO 98/042988(Woodwelding) and WO 2006/002569 (Woodwelding) or WO 2008/080239 a firstapproach is known to anchor inserts including materials havingthermoplastic properties in fibrous or porous materials such as e.g.chipboard or wood. For such anchoring, the insert is positioned relativeto the opening, and then mechanical vibration, in particular ultrasonicvibration, and a force directed for pressing the insert into the openingare simultaneously applied to the insert. In the step of positioning theinsert, no relevant force is used, i.e., on application of the vibratoryenergy, the positioned insert will vibrate freely, or will, due to thenamed force pressing it against the fibrous or porous material, transmitthe vibratory energy to the latter. In the step of applying vibrationand force, the material having thermoplastic properties is liquefied dueto friction heat at least where in contact with the fibrous or porousmaterial and it penetrates into the fibrous or porous material of thewalls of the opening and forms on re-solidification a positive fitconnection with the porous or fibrous material.

According to a second, alternative approach, the second object(including a second material penetrable by a thermoplastic material) maybe chosen to include an opening having a depth and the first object(including a first material being a solid material having thermoplasticproperties) to include an insert portion having a length, wherein theopening and the insert portion are adapted to each other for the insertportion to be positioned in the opening with an interference fit. Inthis, the first and second materials constitute at least part ofopposite surface areas of insert portion and opening pressed againsteach other in the interference fit. The interference fit may then beestablished by placing the insert portion in the opening and applying aninterference force, and only thereafter, the insert portion is anchoredin the opening by transferring energy suitable for liquefaction of thefirst material to the vicinity of said opposite surface areas in anamount and for a time sufficient, for liquefaction of the first materialand interpenetration of the first and second materials in the vicinityof the opposite surface areas and stopping the transfer of energy for atime sufficient for the first material liquefied during the step ofanchoring to re-solidify. The energy may be mechanical vibration energy,in particular ultrasonic vibration.

Especially if the second, alternative approach (with establishing aninterference fit prior to the anchoring step) but also on certainembodiments of the first approach in which during the step of applyingvibration and force, for example described in WO 2008/080239, a slightlyoversized portion of the insert is pressed into the opening, the secondobject may be subject to a considerable mechanical load due to theinterference force. Depending to the composition of the penetrablematerial or possibly other materials of the anvil object, there may be arisk of cracks or other damages (such as portions flaking off) beingcaused by the introduction of the insert portion into the opening priorto the step of anchoring. This risk of such damages is particularly highif the second object is board shaped at least in sections and if theopening is an opening in the narrow side face of the board, inparticular if the dimensions of the opening are of a same order ofmagnitude as the thickness of the board (board section) so that there isnot too much of the penetrable material between the opening and thebroad surfaces. The same applies to objects that are not necessarilyboard shaped if a distance between the opening and a side surface iscomparably small, for example not larger than one or two times anopening diameter.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for joiningtwo objects based on the above-mentioned first or second approach wherethe risk of damages to the second object caused by inserting the insertportion in the opening if the insert portion has a slightly oversizedcross section is minimized.

According to an aspect of the invention, a method of anchoring a firstobject in a second object is provided, the method including the stepsof:

providing the first object including a first material and providing thesecond object including a second material, wherein the first material issolid and includes thermoplastic properties and wherein the secondmaterial is solid and is penetrable by the first material when in aliquefied state, the second object having an end face with an openingwith an opening axis and the first object further including an insertportion,

wherein the opening and the insert portion are adapted to each other forthe insert portion to be positioned in the opening, and wherein saidfirst and second materials constitute at least part of opposite surfaceareas of insert portion and opening pressed against each other,

applying a clamping force to the second object while the insert portionis at least partially inserted in the opening, the clamping force actingbetween two opposing clamping elements arranged so that the opening isbetween the surfaces on which the clamping elements act when theclamping force is applied, the clamping force acting in a directionnon-parallel to the opening axis,

anchoring the insert portion of the first object in the opening bytransferring energy suitable for liquefaction of the first material tothe vicinity of said opposite surface areas in an amount and for a timesufficient, for at least partial liquefaction of the first material andinterpenetration of the first and second materials in the vicinity ofsaid opposite surface areas;

stopping the transfer of energy for a time sufficient for the firstmaterial liquefied during the step of anchoring to re-solidify.

In this, the clamping force may be applied during the step of anchoringor before the step of anchoring (for example, during the step ofestablishing an interference fit, especially by inserting the insertportion in the opening) or both.

The application of the clamping force reduces the risk that cracks areformed in the second object, since the second object is supported by theclamping force during at least a portion of the time during which theinterference fit exerts a mechanical load on the second object. Also,the clamping force reduces the risk of visible bulges of the secondobject.

Whereas in the prior art, clamping is used for holding an object, forexample for transport thereof, the present invention thus suggestsapplying a clamping force specifically—and for example locally—forkeeping an object intact. Due to this, especially the clamping force maybe applied in temporal and spatial correlation with the anchoring and/orthe insertion of the insert portion in the opening.

In embodiments, the opening and the insert portion are adapted to eachother for the insert portion to be inserted with an interference fit.

The fact that the opening and the insert portion are dimensionallyadapted to each other for an interference fit (press-fit) implies thatthe insert portion is oversized at least locally compared with theopening, resulting in at least local pressure between insert portion andopening wall when the insert has a desired position within the opening,i.e. resulting in elastic compression of the insert portion and/or thewall of the opening. Therein the named first and second materials arearranged opposing each other at least in parts of areas of suchcompression.

This feature that the insert portion and the opening are adapted to eachother for the insert portion to be positioned in the opening with aninterference fit may, but does not need to be, used for establishing aninterference fit before the step of anchoring, in accordance with theabove-mentioned second approach. Then, the method includes the furtherstep of establishing the interference fit by placing the insert portionin the opening and applying an interference force, and the step ofanchoring the insert portion is carried out after the step ofestablishing the interference fit.

In such an optional method step of establishing the interference fitfirst, the insert portion is positioned in the desired position withinthe opening where it is retained by the above named interference fit.For achieving the interference fit, i.e. for generating the compressionbetween insert portion and opening wall an interference force isnecessary either for forcing the insert portion into the undersizedopening or for clamping wall sections of the opening against the insertportion. The magnitude of the interference force correspondssubstantially with the strength and area of the interference fit and itis mainly dependent on and limited by the relative dimensions of insertportion and opening and on the compressibility of either one or both ofthe two materials.

In alternative embodiments, no interference fit is established prior tothe anchoring step, but the fact that the insert portion and the openingare adapted to each other for the insert portion to be positioned in theopening with an interference fit merely implies that an interferencecould be established if the insert portion was pressed further into theopening. In these embodiments, the insert portion prior to the anchoringstep is placed relative to the opening only to an extent that nosubstantial force is necessary. During the step of anchoring, the insertportion is further moved relative to the opening, for example by beingpressed further into the opening, until the opposite surface areas ofthe insert portion and the opening are in contact with each other, whileat the same time parts of the first material are liquefied. Thesealternative embodiments are based on the above-mentioned first approach.

In an even further group of embodiments, the insert portion is notoversized compared to the opening, i.e. insert portion and opening arenot adapted to each other for an interference fit. In these embodiments,the anchoring is carried out by a distally facing end face of the insertportion being pressed against a bottom and/or shoulder and/or taper ofthe opening, i.e. the opposite surface areas are thebottom/shoulder/taper of the opening and the according section of theinsert portion pressed thereagainst.

Also in embodiments of this even further group, the approach accordingto the invention may be advantageous because due to the pressing of theinsert portion into the opening and simultaneous liquefaction, ahydrostatic pressure may be built up in the opening, and the clampingforce may counteract adverse effects of this hydrostatic pressure on thefirst object.

In embodiments, the second object has a board shaped section definingtwo broad surfaces and a narrow side face between the broad surfaces,wherein the above-mentioned end face with the opening(s) is the narrowside face of the board shaped section. Especially, the second object maybe a board of a wood-based material, such as chipboard, fiber board,such as High Density Fiber board (HDF) and Medium Density Fiber board(MDF), or wood. In this text “chipboard” is used to refer to anycomposite materials manufactured by mixing wood particles of any shapewith adhesives, independent of the product's shape, including, forexample, oriented strand board.

In embodiments, the clamping force is perpendicular to the opening axis,i.e., the opening extends along a plane perpendicular to the clampingforce. This plane in which the opening axis extends may especially beparallel to the broad surfaces of the board, i.e. to the board plane.

The clamping force may be a force that is constant or follows acontrolled (pre-determined or dependent on measured parameters) timedependent profile, for example by being applied by a pressurized airbased mechanism driven by a suitable compressor and possibly a regulator(including valves etc.). These embodiments feature the advantage ofmaking a precise control and an easy adaptation to changingrequirements—for example due to changing material compositions orelement dimensions—possible.

In embodiments, applying the clamping force is coordinated withtransferring energy and/or with inserting. In many embodiments, theclamping force is maintained until the energy input is sufficient forliquefying at least a part of the insert portion so that the pressuregenerated by the interference fit (if any) is substantially released.

Alternatively, the clamping force may be applied by holding the clampingelements at a fixed position relative to one another during the clampingstep, for example by a mechanical locking mechanism. An embodiment of asuitable mechanical locking mechanism includes a knee lever or similar.

Embodiments that feature holding the clamping elements at a fixedposition relative to one another have the advantage that they may beparticularly simple to set up, with no additional energy input for theclamping force required, and that the clamping force is automaticallyadapted to the circumstances. In configurations with larger expandingforces on the second object (for example, of the insert portion isparticularly strongly oversized compared to the opening), the tendencyto bulge will be larger, but as the clamping elements are at a fixeddistance, the clamping force will if necessary automatically be higher.

The clamping elements may be opposing jaws of a clamp. Alternatively,one of the clamping elements may be a support (such as a panel/table ofa manufacturing machine) and the other one may equipped for beingpressed/held relative to the support.

In a group of embodiments, a clamping surface area (i.e. the area of aninterface between the respective clamping element and the surfaceportion against which it is pressed during clamping) of at least one ofthe clamping elements may be comparably small, for example smaller thanthe surface against which it is pressed (the broad surface in case of aboard shaped second object) by at least a factor 5 or 10.

It has been found that the clamping surface only needs to approximatelycover the insert portion, i.e. in a projection along the direction ofthe clamping force the dimension of the clamping surface does not needto be much larger than the according dimension of the insert portion. Inembodiments, the clamping surface is slightly larger than the accordingdimensions of the insert portion, for example a lateral extension(extension perpendicular to the opening axis) maybe 1.5 to 8 or 2 to 5times a diameter of the insert portion, whereas a longitudinal extension(extension parallel to the opening axis) may correspond to about 1.2 to3 or 1.5 to 2.5 times the length of the insert portion. The conditionmay apply that for at least one of the clamping elements a clampingsurface area corresponds to at most 40 times, preferably at most 20times, and for example at most 15 times, and at least 1.5 times or atleast 2.5 times an area of the insert portion as seen in a projection ona plane being perpendicular to the direction of the clamping force.

It has been found by the inventors that not necessarily the pressingforce needs to be the decisive quantity for the prevention of damagesbut the mechanical pressure. By keeping the area of the clamping surfacearea comparably small, the pressing force required to upheld a certainmechanical pressure is kept comparably small. In embodiments with achipboard board (panel) as the second object and with an insert portionof a diameter of about 10 mm, it has been found that the pressure shouldpreferably be at least about 0.3 or 0.4 N/mm².

Further, the comparably small clamping surface areas make possible thatthe movable mass of clamping elements is comparably small, which may bea further advantage in a high speed process. The handling may beaccelerated while the board remains protected from overly high impactdue to too high clamping element momenta.

Especially, the second object may be provided with a plurality ofopenings at an according plurality of sites (for example spaced fromeach other on the narrow side face if the second object has a boardshaped section) for anchoring a plurality of first objects therein,wherein the clamping force is applied individually for each site insteadof by a large clamp extending over more than one of the sites.Especially, a device for applying the clamping force may include for atleast one of the broad surfaces a plurality of clamping elementsarranged side by side. A machine for carrying out the method may includethe possibility of adjusting the distance between the clamping elements.

In the approach according to the invention, the first material is solid(at ambient temperature) and includes thermoplastic properties (i.e., itis liquefiable with the aid of thermal energy; in the following thismaterial is called “thermoplastic material”),

The second material is also solid and it is penetrable by the firstmaterial when the latter is in a liquefied state (i.e. the secondmaterial is fibrous or porous, it includes penetrable surface structuresor it cannot resist such penetration under pressure). The penetrablematerial especially is rigid, substantially not elastically flexible (noelastomer characteristics) and not substantially plastically deformable.It further includes (actual or potential) spaces into which theliquefied material can flow or be pressed for the anchoring. It is,e.g., fibrous or porous or includes penetrable surface structures whichare e.g. manufactured by suitable machining or by coating (actual spacesfor penetration). Alternatively the penetrable material is capable ofdeveloping such spaces under the hydrostatic pressure of the liquefiedthermoplastic material, which means that it may not be penetrable oronly to a very small degree when under ambient conditions. This property(having potential spaces for penetration) implies e.g. inhomogeneity interms of mechanical resistance. An example of a material that has thisproperty is a porous material whose pores are filled with a materialthat can be forced out of the pores, a composite of a soft material anda hard material or a heterogeneous material (such as wood) in which theinterfacial adhesion between the constituents is smaller than the forceexerted by the penetrating liquefied material. Thus, in general, thepenetrable material includes an inhomogeneity in terms of structure(“empty” spaces such as pores, cavities etc.) or in terms of materialcomposition (displaceable material or separable materials).

Especially, the second material is not only solid at ambienttemperature, but is such that it does not melt under the conditions thatapply when the first material penetrates the surface structures. Forexample, the second material may be of a material that does not havethermoplastic properties, i.e. a material different from a thermoplasticmaterial. The second material may further be such that it does notundergo a reversible liquefaction process or that it has a meltingtemperature substantially above a temperature at which the firstmaterial becomes flowable. For example, if the second material ismeltable, for example if it is a metallic foam, its melting temperatureor glass transition temperature may be higher than a glass transitiontemperature or melting temperature of the first material by at least 50°C. or at least 80° C. or at least 100° C.

In the anchoring step, energy is applied to one or the other of theobjects, wherein the energy is to act as heat, in particular in areas(anchoring areas) in which, in embodiments due to the interference fit,surface areas of insert portion and opening wall are pressed againsteach other and include one each of the thermoplastic and the penetrablematerial. The heat causes the thermoplastic material to liquefy and thepressure of the interference fit and/or the pressure due to the pressingforce causes interpenetration of the two materials, wherein, ifapplicable, the interference fit is at least partly relaxed.

In the last of the above-mentioned method steps, the supply of energy isstopped until the thermoplastic material liquefied and dislocated in theanchoring step is re-solidified, whereby in the interpenetration area asort of composite material is formed, which connects the two objects ina positive fit connection.

The energy necessary for liquefying the thermoplastic material in theanchoring step may be supplied, as above discussed, to either one of thetwo objects. In embodiments, this is done in the form of mechanicalvibration, in particular ultrasonic vibration, to be transformed intofriction heat at the interface between the insert portion and the wallof the opening. The vibration, for example, has a main vibrationdirection parallel to the named opposite surfaces of insert portion andopening wall. Preferred therefore are, for achieving lateral anchorage,longitudinal vibrations substantially parallel to the depth of theopening or rotary vibrations with an axis substantially parallel to thedepth of the opening.

In embodiments that include establishing an interference fit prior toanchoring, for overcoming the interference fit, it is necessary to applya shearing load between the insert portion and the opening wall, whereinthis shearing load may be caused by strong enough vibration of the oneof insert portion or opening wall relative to the other one, or by thevibration and an additional shearing force acting between the twoobjects. For preventing undesired movement, in particular translationalmovement of the two objects relative to each other due to the shearingforce, it may be necessary to counteract the latter in a suitablemanner.

Other sorts of energy such as, e.g., irradiation with electromagneticenergy for which suitable absorbing means are to be provided at thelocations where the interference fit is active, or corresponding heating(e.g., inductive or resistive heating) are applicable also.

The thermoplastic material and the penetrable material taking part inthe anchorage may be present only on selected surfaces of the insertportion and on walls of the opening. For example, the insert portion mayinclude a core of a not thermoplastic material and a coating thereofmade of the thermoplastic material. However, they may also constitutelarger portions of the two objects, which may include further portionsof different materials or may fully consist of either the thermoplasticmaterial or the penetrable material.

In the regions of the opposite surface areas either one of the twosurfaces being pressed together may include structures functioning asenergy directors, i.e. point-shaped or line-shaped elements protrudingfrom a principal surface.

In addition or as an alternative to the approach according to thisinvention that includes applying a clamping force, the method ofanchoring the first object may include using the thermoplastic materialof the first object that has flown during the anchoring step for healingpossible cracks in the second object. This may especially be combinedwith an insert portion design that favors in-plane (along the boardplane) material flow. Examples of such designs are for example describedin the Swiss patent application 01 539/14 in FIGS. 28 and 29 and theirdescription.

Examples of second materials (penetrable materials) are wood-basedmaterials such as chipboard (“chipboard” in this text includes anycomposite materials manufactured by mixing wood particles of any shapewith adhesives, independent of the product's shape, including forexample oriented strand board) or wood, or metallic or ceramic foams orpossibly open porous structures of a material based on a notthermoplastic (thermosetting) polymer. Specific examples of penetrablematerials applicable in the method according to the invention are solidmaterials such as wood, plywood, chipboard, cardboard, concrete brickmaterial, porous glass, foams of metal, ceramic, or polymer materials,or sintered ceramic, glass or metal materials, wherein such materialsinclude spaces into which the thermoplastic material can penetrate,which spaces are originally filled with air or with another displaceableor compressible material. Further examples are composite materials,which have the above stated properties, or materials with surfacesincluding a suitable roughness, suitable machined surface structures orsuitable surface coatings (e.g. consisting of particles). If thepenetrable material has thermoplastic properties it is necessary that itmaintains its mechanical strength during the anchoring step either byfurther including a mechanically stable phase or by having aconsiderably higher melting temperature than the thermoplastic materialto be liquefied in the anchoring step.

A thermoplastic material suitable for the method according to theinvention is, under the conditions of the step of establishing theinterference fit, also solid in the sense as above described for thepenetrable material. It preferably includes a polymeric phase(especially C, P, S or Si chain based) that transforms from solid intoliquid or flowable above a critical temperature range, for example bymelting, and re-transforms into a solid material when again cooled belowthe critical temperature range, for example by crystallization, wherebythe viscosity of the solid phase is several orders of magnitude (atleast three orders of magnitude) higher than of the liquid phase. Thethermoplastic material will generally include a polymeric component thatis not cross-linked covalently or cross-linked in a manner that thecross-linking bonds open reversibly upon heating to or above a meltingtemperature range. The polymer material may further include a filler,e.g. fibers or particles of material that has no thermoplasticproperties or has thermoplastic properties including a meltingtemperature range that is considerably higher than the meltingtemperature range of the basic polymer.

Examples for the thermoplastic material applicable in the methodaccording to the invention are thermoplastic polymers, co-polymers orfilled polymers, wherein the basic polymer or co-polymer is e.g.polyethylene, polypropylene, polyamides (in particular Polyamide 12,Polyamide 11, Polyamide 6, or Polyamide 66), Polyoxymethylene,polycarbonateurethane, polycarbonates or polyester carbonates,acrylonitrile butadiene styrene (ABS), Acrylester-Styrol-Acrylnitril(ASA), Styrene-acrylonitrile, polyvinyl chloride, polystyrene, orPolyetherketone (PEEK), Polyetherimide (PEI), Polysulfon (PSU),Poly(p-phenylene sulfide) (PPS), Liquid crystall polymers (LCP) etc.LCPs are of particular interest since their sharp drop in viscosityduring melting enables them to penetrate in very fine spaces in thepenetrable material.

Usually either one of the two objects to be joined needs to be able totransfer the vibration energy, preferably with a minimum of energy loss,from a proximal object side, where a vibrating tool is applied, to adistal side, where the insert portion or the opening is arranged. Ifthis object is fully made of the thermoplastic material the latter willneed an elasticity coefficient (at ambient temperature) of at least0.5.GPa or preferably of at least 1.0 GPa.

Mechanical vibration or oscillation suitable for the method according tothe invention has preferably a frequency between 2 and 200 kHz (evenmore preferably between 10 and 100 kHz, or between 20 and 40 kHz) and avibration energy of 0.2 to 20 W per square millimeter of active surface.The vibrating tool (e.g., sonotrode) is, for example, designed such thatits contact face oscillates predominantly in the direction of the toolaxis (longitudinal vibration) and with an amplitude of between 1 and 100μm, preferably around 30 to 60 μm. Such preferred vibrations are, e.g.,produced by ultrasonic devices as known from ultrasonic welding.

The invention also concerns a machine for carrying out the method. Sucha machine includes an insertion mechanism capable of inserting theinsert portion at least partially in the opening, an anchoring toolcapable of transferring the energy suitable for liquefaction of thefirst material to the first object or the second object, or both, forthe anchoring step, and further includes a clamping mechanism capable ofapplying the clamping force to the second object during insertion oranchoring or both.

The machine may include an insertion station and an anchoring stationseparate therefrom, wherein the clamping mechanism is capable ofapplying the clamping force at least in the anchoring station.

Alternatively, it may be equipped for carrying out the steps ofinserting and of anchoring at a same station. In such embodiments, themachine may include a gripping arrangement adapted for holding the firstobject in place for insertion, for example without substantial force,wherein the anchoring tool is adapted for contacting the first objectadjacent to the gripping arrangement and for inserting the insertionportion into the opening.

For carrying out the process simultaneously for different first objects(for example, fittings) at different anchoring sites of a same (orpossibly different) second object, the machine may include a pluralityof clamping elements defining an according number of clamping sites thatcorrespond to the anchoring sites. For carrying out the method fordifferent second objects, a distance between the clamping sites may beadjustable.

At least one of the clamping elements of the machine may include anon-sticking arrangement adapted for facilitating release of theclamping element from the second object after release of the clampingforce. In embodiments, said non-sticking arrangement includes anon-sticking pad, for example made from low friction material, and/or agas supply for supplying release gas to a position between the clampingelement and the second object.

In a group of embodiments, the machine further includes a pressurizedfluid cylinder, such as a pressurized gas (for example, pressurized air)cylinder or a hydraulic cylinder, for applying the clamping force on theclamping element.

A pressurized gas cylinder may also be present for attenuating/levelingthe clamping force, especially in case of mechanical lockingarrangements if otherwise damages to the surface of the second objectare to be expected caused by too high pressures.

Applications of the concepts described in this text and illustrated inthe figures include the furniture industry, especially furnituredesigned for self-assembly by the customer. In this, the first objectmay be a fitting, and the second object may be a furniture part with aboard-shaped section.

Further applications include other branches of mechanical engineeringand constructions, including the automotive, aviation and shipbuildingindustries where the method may be suitable of anchoring an anchor in alightweight board of any composition, building industry, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and embodiments thereof are described in further detail inconnection with the appended drawings that are all schematical. Samereference numbers refer to same or analogous elements. In the drawings:

FIG. 1 illustrates an embodiment of the method according to theinvention;

FIG. 2 shows an example with the clamping force being appliedsimultaneously to two anchoring sites;

FIGS. 3a and 3b show a further example with the clamping force beingapplied simultaneously to two anchoring sites;

FIG. 4 illustrates a clamping element with a non-sticking pad

FIG. 5 illustrates using pressurized air for preventing any sticking;

FIGS. 6 and 7 illustrate clamping surface areas;

FIGS. 8 and 9 show examples for the application of pressure, vibrationand clamping force as a function of the time;

FIG. 10 illustrates a principle of applying the clamping force by a kneelever mechanism;

FIG. 11 illustrates the principle of applying the clamping forcesimultaneously to two anchoring sites by a machine with clampingelements having a variable distance;

FIG. 12 shows the principle of inserting and subsequently anchoring thefirst object at a same station;

FIG. 13 shows the principle of inserting and subsequently anchoring thefirst object at subsequent stations; and

FIG. 14 illustrates a second object with a stepped cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a board 1 of for example chipboard being the secondobject in a method according to the invention. The board has two opposedbroad surfaces 3 and a narrow side face 4 with a blind opening 2. Afitting element 5 having a head portion 8 and an insert portion 6 servesas the first object in the method. The fitting element 5 in the depictedembodiment includes a thermoplastic material, for example a polyamideand is, according to an embodiment, made entirely or almost entirelyfrom this thermoplastic material, whereas in alternative embodiments itmay include a core of a not thermoplastic material with a coating of athermoplastic material.

The insert portion 6 has a slightly oversized cross section compared tothe opening 2 so that the insert portion is held in an interference fitin the opening 2 after the insert portion 6 has been introduced, forexample by a pressing force acting in a direction of an axis 20 of theopening. Due to the interference fit, opposite surface areas 18, 19 ofthe insert portion 6 and the opening 2 are pressed against each other.In the subsequent anchoring step, a vibrating tool, namely a sonotrode11 is used to couple mechanical vibration energy into the fittingelement 5 to liquefy portions of the thermoplastic material of thefitting element 5, and preferably of the insert portion 6, that thenpenetrate into structures of the board 1 and yield, after the energyinput stops, the above-described anchoring.

During the step of inserting and/or during the step of anchoring aclamping force is applied to the site where the anchoring takes place.In the depicted configuration, the clamping force is applied between amovable clamping element 21 and a support 22 serving as a secondclamping element.

In embodiments that include establishing an interference fit, and inwhich the clamping force is applied during both steps, the clampingforce serves for strengthening the second object 1 including the opening2 (or a plurality of openings) and the penetrable material for betterwithstanding the establishment of the interference fit and the anchoringstep. Also in embodiments that do not include the step of establishingthe interference fit prior to the step of anchoring but in which theoversized section of the insert portion is only introduced during theapplication of the mechanical vibration, a similar strengtheningresults.

The clamping force to be applied may, for example, be achieved byconnecting the movable clamping element 21 to, for example, apressurized gas or air cylinder 16, as schematically sketched, ahydraulic cylinder, or a mechanic screw. In particular air cylinders andhydraulic cylinders are convenient in that the clamping pressure may becontrolled by controlling the air- or hydraulic pressure.

FIG. 2 illustrates such an example of strengthening the first object 1including the opening 2 (or a plurality of openings) and the penetrablematerial for better withstanding the establishment of the interferencefit and the anchoring step. The object 1 again is, e.g., a chipboard andthe openings extend from a narrow side thereof. FIG. 2 shows the board 1viewed in the direction of its narrow side 4, and illustrates: on theleft hand side: before the step of establishing the interference fit, inthe middle: between the step of establishing the interference fit andthe anchoring step, and on the right hand side: after the anchoringstep. Prior to the step of establishing the interference fit, the boardis strengthened by being clamped together with a pair of clamping jaws21, 22. The clamping prevents bulging outwards of the board broadsurfaces 3 on establishing the interference fit and such weakening thelatter. This means that the clamping allows establishing a strongerinterference fit than would be possible without it and therefore astronger anchorage. As the stress of the interference fit issubstantially relaxed during the anchoring step, since in the anchoringstep the thermoplastic material of the fitting element 5 is at leastpartly liquefied, the clamping can be released after the anchoring step.

The depicted configuration of FIG. 2 is an example of the clampingelements covering a plurality of anchoring sites, i.e. a plurality ofopenings is between two clamping elements 21, 22. However, it is alsopossible, and often advantageous, to apply the clamping forcesimultaneously or one after the other to a plurality of clamping siteswith separate clamping elements. FIG. 3a shows an example of a board 1,viewed in the direction of its broad side 3, that includes fouranchoring sites 26, 27, 28, 29. For the step of establishing theinterference fit (if any) and/or for the step of anchoring, a pluralityof first, movable clamping elements 21 is used. In the depictedconfiguration, the anchoring sites 26, 27, 28, 29 are arranged at twoopposed narrow side faces. Therein, at least the clamping andinterference fit establishing/anchoring steps for the (two) anchoringsites 26, 27; 28, 29 of the same narrow side face 4 may be donesimultaneously, with the possibility of carrying out the according stepsimultaneously for all four sites 26, 27, 28, 29.

As shown in FIG. 3b , in which the board 1 is viewed from one of itsnarrow side faces 4, the respective opposed clamping elements may besecond clamping elements 25 on a support 24. It is also possible todirectly place the board 1 on such a support 24 (which then serves asclamping element), or to use second clamping elements that are alsomovable and for example belong to a clamping jaw.

As the clamping elements are to exert a considerable pressure on theboard 1 (in an example with chipboard as the penetrable material andwith fittings 5 having an insert portion 6 of a diameter of about 7 mm,the necessary clamping pressure has been found to exceed 0.4 N/mm²),depending on the surface properties of the board 1 there may be acertain risk of the clamping elements 21, 25 sticking to the broadsurfaces when the clamping pressure is to be released. To this end, theclamping elements 21, 25 may be provided with a non-sticking pad 32 orsurface coating, as schematically illustrated in FIG. 4. Such anon-sticking pad 32 or surface coating may, for example, include PTFE,for example sold under the trademark Teflon. The non-sticking pad 32 orsurface coating may be held by a clamping element body 31 ofconventional machinery material, such as stainless steel.

A further possibility of dealing with the risk of sticking is shown inFIG. 5, where a clamping element 21 is provided with an air channel 35opening towards the broad surface 3 of the board 1 and through whichpressurized air is blown after the clamping process to release the clamp21 from the broad surface 3 of the board 1.

FIG. 6 illustrates the principle of a clamping surface area optimizedfor the process. The interpenetration zone 41, in which a sort ofcomposite material is formed as the thermoplastic material is liquefied,has, in a projection perpendicular to the broad side plane, an areaslightly exceeding the dimension of the insert portion 6. Depending onthe requirements, it may be advantageous that the clamping surface 42covers the interpenetration zone 41 and extends somewhat beyond it. Insituations, it may be advantageous if the clamping surface 42 (incontrast to what is shown in the schematic illustration of FIG. 1)extends to the edge between the broad surface 3 and the narrow side face4 because in some materials this edge is particularly prone to damages.The area of the clamping surface 42 is preferably smaller than the totalarea of the broad surface 3, which faces the clamping element 21 andagainst which the clamping element 21 is pressed, by at least a factor5.

Whereas in FIG. 6 the clamping surface 42 is illustrated to berectangular, other shapes of clamping surfaces 42 are possible,including trapezoid as shown in FIG. 7. In FIG. 7, the edge of the boardis assumed to be on the right hand side (same orientation as FIG. 6).

FIGS. 8 and 9 illustrate the possibility of coordinating the clampingpressure with the insertion and/or the mechanical energy input (in FIG.8, U denotes the input power of ultrasonic vibration, P the pressure; inFIG. 9 F_(i) is an interference force and F_(c) a clamping force, thex-axis corresponds to the time in both figures).

As sketched in FIG. 8, the clamping pressure 51 may set in prior to themechanical energy input 52. This may, for example, be advantageous incase, as further described hereinafter, the insertion and, ifapplicable, establishing an interference fit is carried out at a samestation. In this case, the clamping force may set in at, or just before,the time the insert portion starts being pressed into the opening. If nointerference fit is established prior to anchoring, the clamping forcemay be lower initially or set in only when the anchoring step starts.The energy input may stop prior to the clamping force being released (52a), at the same time or thereafter (52 b). In the latter case, withenergy input stopping after the clamping force being released (52 b), itis beneficial that clamping force is not released before liquefactionand infiltration has caused a substantial reduction in the interferenceforce.

FIG. 9 shows that the interference force 54 may relax as a consequenceof the liquefaction process, and the clamping force 55 may stop aftersuch relaxation. The onset of the respective forces is illustrated to besynchronized. Synchronization may be optimized to minimize the lag time.

As shown, the interference force can initially be higher than theclamping force as long as the crossover of both curves is below thedamage threshold of the board material.

Furthermore, since the board material has an certain initial resistanceagainst splitting—the clamping force does not need to be higher than theinterference force, actually, only the sum of clamping force, damagethreshold and some safety margin has to be higher than the interferenceforce.

Instead of applying a constant pressure or a pressing force/pressureprofile, the clamping force may be applied by holding the clampingelements at a fixed position relative to one another during the clampingstep. Then, the clamping force may be zero or very small until theinsertion of the insert portion starts exerting an expanding force onthe board.

FIG. 10 very schematically shows an according mechanism employing theabove mentioned fixed position. The clamping element 21 is held by aknee lever including a first lever arm 61.1 and a second lever arm 61.2,the second lever arm connected to a counter element 64 that, forexample, together with a support 22 may form a load frame and may beheld at a fixed distance to the support 22. At the onset of the process,the knee joint is brought into its correct position, for example bybeing moved (by any suitable means) into the direction of the arrow. Astop 65 is illustrated at a position in which the knee lever is movedslightly over the neutral point, so that the knee lever becomesself-locking and no external force needs to be applied for clamping.

Other locking mechanisms locking a distance between two clampingelements are possible.

FIG. 11 illustrates schematically the possibility of providing amanufacturing machine with clamping elements 21 having a variable,adjustable distance D. Thereby, the machine becomes very flexible forinserting parallel fitting elements 5 at different mutual distances D,and still see to it that clamping is achieved, by means of the clampingelements 21, at the relevant locations, i.e. in the current position ofthe fitting elements 5.

As previously mentioned, a machine for carrying out the method mayinclude means for inserting the insert portion in the opening and meansfor carrying out the anchoring step at a same station or at differentstations. FIG. 12 shows a station for performing both, the insertingstep and the anchoring step.

A gripper 71 is used for holding the first object (fitting element 5) inplace for insertion, substantially without exerting pressure. Thesonotrode 11 exerts the pushing force for the insertion step until theinsert portion 6 is inserted in the opening 2 to a sufficient depth forthe fitting element 5 being held therein. If applicable, the pressingforce is exerted until the interference fit is established.

The gripper 71 is then removed, and, for the anchoring step, thesonotrode 11 starts coupling mechanical energy into the fitting element5 while still or again exerting a pressing force. The clamping force isexerted by means of the clamping element 21 and the support 22 duringthe anchoring step and/or during the insertion step, preferably duringboth the insertion step and the anchoring step.

FIG. 13 illustrates a machine with two stations, namely an insertionstation 81 in which first objects (here: fitting elements 5) areinserted into openings 2 of a second object (here: board 1), and ananchoring station 82 in which sonotrodes 11 apply mechanical vibrationenergy to the fitting elements 5. After insertion of the fittingelements 5 into the board 1 at the insertion station 81, the board 1 ismoved to the anchoring station 82 where the anchoring process is carriedout. Generally, for embodiments with different stations for insertionand anchoring (not only in the depicted configuration), the followingpossibilities apply:

-   -   In accordance with a first possibility (illustrated in FIG. 13),        there is no clamping element at the insertion station 81. The        clamping force, applied by means of, e.g., clamping elements 21,        is only applied for the anchoring process in the anchoring        station 82.    -   In accordance with a second possibility, a clamping force is        applied during the insertion step performed at the insertion        station 81, the clamping force is, then released and is again        applied for the anchoring step performed at the anchoring        station 82.    -   In accordance with a third possibility there is no clamping        element at the anchoring station 82. The clamping force is only        applied for the insertion process in the insertion station 81.    -   In accordance with a fourth possibility, a clamping force is        applied at the insertion station 81, and it is upheld during        movement and, at least initially, during the anchoring step        performed at the anchoring station 82. This may for example be        done by a mechanical clamp mounted to the board at the insertion        station 81 and then moving along with the board 1, wherein the        mechanical clamping is released at the anchoring station 82,        after at least a part of the liquefaction of the insert portion        6. Alternatively, a clamping mechanism that moves along with the        board 1 may be provided. In this case, the clamping mechanism        may optionally at the same time hold the board 1 and carry out,        or contribute to, the relative movement from the insertion        station 81 to the anchoring station 82.

FIG. 14 illustrates a second object with a stepped cross section of theinsertion portion 6 of the fitting element 5. The first cross section(diameter d₁) approximately corresponds to the cross section of theopening 2 in the board 1 or is slightly smaller than it so that theaccording first insertion portion section 6.1 may be introduced into theopening 2 without substantial interference force being exerted on theboard 1. The second cross section (diameter d₂) is oversized, meaningthat the second cross section, being the cross section of the secondinsertion portion section 6.2, is larger than the cross section of theopening 2 in the board 1 so that inserting this second insertion portionsection 6.2 provides for an interference fit. In a machine according tothe above-mentioned first possibility, the insertion station mayintroduce the insert portion only to the extent illustrated in FIG. 14,i.e. so that there is no substantial interference force. This makes thestepped cross section (or other cross sections that at least locally arelarger at more proximal positions than at more distal positions)attractive in combination with methods/machines in which there is noclamping at an insertion station, as there will be a need for clampingfirst at the subsequent anchoring station when the second insertionportion section 6.2 is forced into the opening 2 by means of thesonotrode.

1. A method of anchoring a first object in a second object, the method comprising the steps of: providing the first object comprising a first material and providing the second object comprising a second material, wherein the first material is solid and comprises thermoplastic properties and wherein the second material is solid and is penetrable by the first material when in a liquefied state, the second object having an end face; wherein the second object further comprises an opening having a mouth in the end face, the opening having an opening axis and a depth and the first object further comprising an insert portion having a length, wherein the opening and the insert portion are adapted to each other for the insert portion to be positioned in the opening, and wherein said first and second materials constitute at least part of opposite surface areas of insert portion and opening capable of being pressed against each other, applying a clamping force to the second object while the insert portion is at least partially inserted in the opening, the clamping force acting between clamping elements acting on opposing surfaces arranged so that the opening is between opposing surfaces when the clamping force is applied, the clamping force acting in a direction non-parallel to the opening axis, anchoring the insert portion of the first object in the opening by transferring energy suitable for at least partial liquefaction of the first material to the vicinity of said opposite surface areas in an amount and for a time sufficient, for liquefaction of the first material and interpenetration of the first and second materials in the vicinity of said opposite surface areas; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify.
 2. The method according to claim 1, wherein the step of applying a clamping force is carried out at least during an initial stage of the step of anchoring.
 3. The method according to claim 1, wherein the opening and the insert portion are adapted to each other for the insert portion (6) to be positioned in the opening with an interference fit, and wherein the opposite surface areas of insert portion and opening are pressed against each other in the interference fit.
 4. The method according to claim 3, comprising the further step of establishing the interference fit by placing the insert portion in the opening and applying an interference force prior to the step of anchoring.
 5. The method according to claim 4, wherein the step of applying a clamping force is carried out at least during an initial stage of the step of establishing the interference fit.
 6. The method according to claim 5, wherein the step of applying a clamping force is carried out continuously during the step of establishing the interference fit and continuing also during at least an initial stage of the step of anchoring.
 7. The method according to claim 1, wherein the second object has a board shaped section defining two broad surfaces and a narrow side face between the broad surfaces, wherein said end face is the narrow side face of the board shaped section.
 8. The method according to claim 1, wherein the direction of the clamping force is perpendicular to the opening axis.
 9. The method according to claim 1, wherein the clamping force is controlled by controlling a pressure of a gas or fluid exerting its pressure on the clamping element.
 10. The method according to claim 1, wherein a clamping pressure exceeds 0.4 N/mm2.
 11. The method according to claim 1, wherein, in the step of anchoring, the transferred energy is mechanical vibration energy.
 12. The method according to claim 1, wherein the clamping force is constant or follows a controlled time dependent profile, wherein preferably the clamping force is controlled so as to be released after an interference force has been reduced.
 13. The method according to claim 1, wherein the clamping force is applied by holding the clamping elements at a fixed position relative to one another.
 14. The method according to claim 13, comprising holding the clamping elements at the fixed position relative to one another by controlling a knee lever comprising a first lever arm and a second lever arm connected to at least one of the clamping elements.
 15. The method according to claim 1, wherein for at least one of the clamping elements a clamping surface area, which is an area of an interface between said clamping element and a surface portion of the second object against which it is pressed during clamping, is smaller than the surface against which it is pressed by at least a factor 5, preferably by at least a factor
 10. 16. The method according to claim 1, wherein for at least one of the clamping elements a clamping surface area corresponds to at most 20 times, preferably at most 15 times an area of the insert portion as seen in a projection on a plane perpendicular to a direction of the clamping force, and preferably at least 1.5 times, or at least 2.5 times said area of the insert portion as seen in a projection on a plane perpendicular to the direction of the clamping force.
 17. The method according to claim 1, wherein the second object has a plurality of openings, the step of providing the first object comprising providing a corresponding number of first objects, wherein the step of applying the clamping force comprises applying the clamping force for each of the openings individually, simultaneously or in sequence.
 18. The method according to claim 1, comprising the step of at least partially inserting the insert portion in the opening prior to the step of anchoring, wherein during the step of anchoring the second object is at a substantially same location as during the step of inserting.
 19. The method according to claim 1, comprising the step of at least partially inserting the insert portion in the opening, and further comprising moving the second object from an insertion station to an anchoring station after the step of inserting and prior to the step of anchoring.
 20. The method according to claim 19, comprising applying the clamping force during the step of at least partially inserting the insert portion and maintaining the clamping force applied at least until the step of anchoring sets in, preferably keeping the clamping force applied during at least a portion of the anchoring step.
 21. The method according to claim 1, wherein in the step of applying the clamping force, the clamping force two clamping elements are opposing and arranged so that the opening is between the clamping elements.
 22. The method according to claim 1, wherein the second material is one of fibrous, porous, comprising penetrable surface structures, and not able to resist penetration on application of pressure.
 23. The method according to claim 1, wherein the second material is one of chipboard, wood, fibre board, plywood and cardboard.
 24. The method according to claim 1, wherein the first material comprises a thermoplastic polymer with an elasticity coefficient of at least 0.5 GPa.
 25. A machine for carrying out the method according to claim 1, comprising an insertion mechanism capable of inserting the insert portion (6) at least partially in the opening, an anchoring tool capable of transferring the energy suitable for liquefaction of the first material to the first object or the second object, or both, for the anchoring step, and further comprising a clamping mechanism capable of applying the clamping force to the second object during insertion or anchoring or both.
 26. The machine according to claim 25, comprising an insertion station and an anchoring station separate therefrom, wherein the clamping mechanism is capable of applying the clamping force at least in the anchoring station.
 27. The machine according to claim 26, being equipped for carrying out the steps of inserting and of anchoring at a same station.
 28. The machine according to claim 27, further comprising a gripping arrangement adapted for holding the first object in place for insertion, wherein the anchoring tool is adapted for contacting the first object adjacent to the gripping arrangement and for inserting the insertion portion into the opening.
 29. The machine according to claim 25, comprising a plurality of clamping elements defining an according number of clamping sites, wherein a distance between the clamping sites is adjustable.
 30. The machine according to claim 25, wherein at least one of the clamping elements is provided with a non-sticking arrangement adapted for facilitating release of the clamping element from the second object after release of the clamping force, preferably said non-sticking arrangement comprising a non-sticking pad, for example made from low friction material, and/or a gas supply for supplying release gas to a position between the clamping element and the second object.
 31. The machine according to claim 25, wherein the machine further comprises a pressurized fluid cylinder, such as a pressurized gas cylinder or a hydraulic cylinder, for attenuating the clamping element. 